1. Field of the Invention
The present invention relates to the field of reinforcing fibres and of composites and, in particular, to the deposition of size compositions on glass filaments (or yarns).
2. Description of the Background
The manufacture of reinforcing glass yarns is carried out, in a known way, starting from streams of molten glass flowing out of the orifices of spinnerets. These streams are drawn in the form of continuous filaments, and these filaments are then converged into base yarns, which are then collected.
Before they are converged into the form of yarns, the filaments are coated with a size by passing over a sizer. This deposition is necessary for obtaining the yarns and allows them to be combined with other organic and/or inorganic materials in order to produce composites.
The size firstly acts as a lubricant and protects the yarns from the abrasion that results from high-speed friction between the yarns and various devices during the aforementioned process.
The size may also, especially after it has cured, provide with the aforementioned yarns integrity, i.e. the mutual bonding of the filaments within the yarns. This integrity is especially desired in textile applications in which the yarns are subjected to high mechanical stresses. This is because, if the filaments are poorly held together, they break more easily and disrupt the operation of the textile machinery. What is more, non-integrated yarns are considered to be difficult to handle.
However, the size is also employed in cases in which this integrity is not desired, such as in the case of reinforcing fibres, when a high rate of impregnation with the material to be reinforced is desired. Thus, in the manufacture, for example, of pipes using direct impregnation and filament winding techniques, open yarns in which the filaments are separated from one another are used. Small quantities of size, especially less than 0.5% by weight, are then used.
The size also facilitates the wetting and/or impregnation of the yarns by the materials to be reinforced and helps to create bonds between the said yarns and the said materials. The mechanical properties of the composites obtained from the material and from the yarns depend in particular on the quality of the adhesion of the material to the said yarns and on the ability of the said yarns to be wetted and/or impregnated by the said material.
Most sizes currently used are aqueous sizes which are simple to handle but which must be deposited in large quantities on the filaments in order for them to be effective. Water generally represents more than 90% by weight of these sizes (especially for viscosity reasons), and this means that the yarns have to be dried before they are used, it being possible for water to impair the good adhesion between the yarns and the materials to be reinforced. These drying operations are lengthy and expensive and their effectiveness is not always optimal; they require the use of large-capacity ovens. In addition, when they are carried out during the fibre-forming operation (that is to say before the yarns obtained by converging the filaments have been collected), either on filaments (WO 92/05122) or on yarns (U.S Pat. No. 3,853,605), they require the installation of dryers under each spinneret and, when they are carried out on yarn packages, they run the risk of causing irregular and/or selective migration of the components of the size within the packages (aqueous sizes already have a tendency to be distributed over the yarns in an irregular manner because of their nature) and possibly of causing yarn-coloration or package-distortion phenomena. Moreover, without drying, package distortion is often observed on straight-sided packages (rovings) of fine yarns (i.e. yarns having a "count" or "linear density" of 300-600 tex (g/km) or less) which are coated with aqueous sizes.
It is to remedy these drawbacks that a novel type of size, which is virtually free of solvents and called an anhydrous size, has been developed. Anhydrous sizes are curable and/or crosslinkable solutions which optionally contain organic solvents and/or water in small amounts, generally of less than 5% by weight. They are distinguished advantageously from aqueous sizes by their ability to be distributed in a homogeneous and uniform manner on the surface of the filaments, i.e. forming films of constant thickness, and by the fact that they make any subsequent drying or solvent-removal treatment unnecessary since the small quantities of solvent evaporate during deposition of the size on the filaments and during curing of the size.
Furthermore, the quantities of anhydrous size deposited on the filaments are much less than those of aqueous size; thus, when depositing by means of a sizing roller, a film is formed on the surface of the latter with a thickness not exceeding 15 .mu.m in the case of an anhydrous size instead of a film with a thickness of approximately 90 .mu.m in the case of an aqueous size. Moreover, these small quantities of anhydrous size are deposited on the filaments with a much higher efficiency, possibly reaching 100% when the operating conditions are chosen judiciously, whereas this efficiency is generally about 40 to 75% with aqueous sizes.
Anhydrous sizes fall mainly into three categories.
The first category encompasses UV-curable sizes as described in Patent EP 0,570,283 and comprising, for example:
at least one mono-unsaturated or polyunsaturated monomer and/or oligomer of the polyester acrylate, epoxy acrylate, silicone compound or urethane acrylate type; PA1 at least one photoinitiator, such as benzoin, acetophenone, benzophenone, sulphonylacetophenone and their derivatives, as well as thioxanthones; PA1 if necessary, at least one organic solvent; and, optionally, PA1 additives such as at least a wetting agent, an adhesion promoter, an anti-shrinkage agent, a compatibilizer consisting especially of a silane. PA1 an acrylic component and a heat-activated radical-initiating peroxide; or PA1 an epoxy component and an anhydrous constituent which cure by reacting with each other. PA1 in continuously impregnating a mat of mechanically held-together fibres, such as a felt or a woven fabric, with the mixture in the liquid state; PA1 in continuously taking up at least some of the said mixture by means of a rotating roller in contact with the said mat; and PA1 using the sizing roller, in depositing the said mixture on the filaments while they are being drawn.
The second family of anhydrous sizes is that of thermally curable and/or crosslinkable sizes, as described in Patent Applications FR 93/14792 and 96/00067.
By way of example, the basic system of these compositions comprises:
The third category of anhydrous sizes forms part of the teaching of Applicant FR 97/05926: these are room-temperature curable sizes, the basic systems of which may contain one or more homopolymerizable monomers and/or at least two copolymerizable monomers which require no external supply of energy. In the case of copolymerization of two monomers, these may be deposited on the filaments in the form of their mixture in solution, immediately after this mixture has been formed, or in the form of a first stable solution containing a first monomer mixture and of a second stable solution containing a second monomer mixture. In the latter variant, the first solution is applied to the filaments and the second is applied subsequently thereto, at the latest while the filaments are being combined into yarns. Be that as it may, the copolymerization generally starts on the filaments as soon as the first and second monomers come into contact with each other and, if necessary, with the required catalyst or catalysts.
The UV-radiation treatments and heat treatments required to cure the sizes of the two first types mentioned above are carried out in one step or in several steps, after the filaments have been converged into yarns. Thus, depending on the envisaged use and on the nature of the yarns, an irradiation or heat pretreatment is sometimes carried out at the time of collecting the yarns in various forms of packages, in order to precure the size, the actual curing of which is carried out in a subsequent radiation or heat treatment when the yarn is unwound for the specific application for which it is intended, namely a textile application or an application of reinforcing organic or inorganic materials. This is because the yarn coated with the as yet uncured composition does not exhibit integrity in the ordinary sense of the term since the sheathed filaments of which the yarn is composed may slip over each other. This yarn can therefore be handled easily and, when it is wound in the form of packages, can be easily extracted from the packages without first having to undergo a treatment to cure the size. The yarn coated with the as yet uncured size composition has, moreover, a very high capability of being wetted and impregnated by materials to be reinforced, it thus being possible for impregnation to take place more rapidly (increase in productivity) and the composites obtained thus having a more homogeneous appearance and having certain of their mechanical properties improved.
However, as described in Patent EP-0,570,283, curing the size by the UV irradiation of a yarn in the form of a package may also have advantages.
With regard to depositing anhydrous sizes on glass filaments, several techniques are known. Thus, according to Application FR 97/05926 already mentioned, this deposition is carried out with the aid of a roller or of a sprayer, with the aid of a device which also acts as a converging means, or by the use of other yarns or filaments coated with the composition and brought into contact with the glass filaments. The latter technique makes reference to the special case of producing composite yarns, consisting of comingled glass filaments and thermoplastic polymer filaments or yarns.
By definition, deposition by spraying is inevitably accompanied by quite a significant amount of loss of size; the recovery of this lost proportion, assuming that it is possible, constitutes a handicap.
The method of deposition by means of a roller or of a device for converging the filaments into yarns consists of taking up size from a somewhat viscous and thick liquid film formed on a smooth surface, having ranges of physical properties, especially surface hardness and surface microporosity, of the type of those of metal surfaces. Starting from the observation that the chemical nature of the anhydrous sizes allows them to be used in ever lower quantities, there is currently a requirement for a process for forming an ever thinner liquid film, of perfectly uniform, controllable and reproducible thickness, on a macroscopicaly smooth surface of the metallic, ceramic or organic type. This is because it may be expected that the take-up of size onto the filaments from such a film results in the filaments being coated with a minimum quantity of size, with an increased deposition efficiency, i.e. a reduction in the amount of size lost, and for this to be achieved under completely controlled conditions. Finally, the aim is, of course, to obtain filaments and yarns, and reinforced materials containing them, which have sufficient, or at least preserved, mechanical properties or even in certain respects novel mechanical properties.
Currently, there is no process making it possible to form, in a controllable manner, a thin film of anhydrous size at the surface, for example, of a metal roller. This is because the immersion of the lower part of the roller in the size solution coupled with the rotation of the roller results in the formation, at the surface of the roller, of a layer whose characteristics can be controlled only to a small extent by varying the viscosity of the solution and the rate of rotation of the roller. The thickness of this layer is too great and irregular, and it is impossible to avoid loss of size, in the device for converging the filaments into yarns or for collecting the yarns, by the size being thrown off the yarns under the effect of the inherent centrifugal force at the high winding rates employed.
Moreover, no system for depositing size on a sizing roller with the aid of a metering pump and of an injection nozzle has yet allowed the formation of the desired film.
Furthermore, the previously-mentioned Patent EP 0,570,283 briefly mentions, in its part describing FIG. 1, a coating device 13 consisting of an applicator provided with a felt moistened with a reactive mixture using a metering pump. This is because the structure of a felt allows it to soak up a solution in a particularly homogeneous manner. However, the take-up of size suggested by the European patent, from the felt onto the glass filaments, is not satisfactory in the context of the technical problem mentioned above since the deposition of the required small quantities of size on the filaments could not be achieved except at the cost of the felt drying out somewhat, a situation which, given the naturally irregular structure of the felt, the surface of which has fibres of varied dimensions, directions or even textures, would run the risk of the glass filaments catching thereon and therefore the risk of the said filaments breaking. Only relatively large amounts of size can thus be deposited in the manner described in the document.